In this work we investigate and discuss the morphological properties and composition of Erbium - doped silica spheres, which can have interesting applications in bioimaging and biosensing. The base catalyzed reaction fails to fabricate Er – doped silica spheres because the RE ions immediately form an insoluble RE hydroxide. For this reason, an acid catalyzed reaction was used to form erbium – doped silica spheres. The molar composition of TEOS : CH3COOH : H2O was 1:4:4. Ebium ions was incorporated in the SiO2 by replacing the water by an aqueous solution of ErCl3.6H2O . To avoid the polydispersible Er – doped silica spheres made by an acid catalyzed method, we use a base catalyzed reaction to fabricate a pure SiO2 core with size about 600nm, after that a shell containing erbium was created by an acid catalyzed reaction. The morphology of Er – doped silica spheres was examined by Scanning electron microscopy (SEM) images and the appearance of erbium was examined by Energy Dispersive X – ray fluorescence spectrometer (EDXRFS).